Extractability and phytoavailability of cadmium in Cd-rich pedogenic soils

Abstract

Conspicuous vegetation entities of pedogenic soils rich in cadmium and their diethylene triamine pentaacetic acid (DTPA)-extractable Cd content (DCd) under the temperate continental and Mediterranean climatic conditions of western Anatolia were determined. Foliage of herbaceous plants and nearby soil samples was collected from 51 zinc mining areas. DCd content was found to reach 11.6%-16.2% of the total Cd content, indicating more extractability than in many other heavy metals. Growth chamber and nursery experiments were conducted with the seeds collected. Dactylis glomerata and Galium tenuissimum subsp. tenuissimum, both common in grazing lands, were found to be accumulating 23.5 mg Cd kg-1 and 22.3 mg Cd kg-1 dry matter, respectively, which are highly phytotoxic levels. Thlaspi praecox, known as a Cd-hyperaccumulating plant species, could not be successfully introduced into the Cd-rich mining soils under controlled conditions, suggesting genetic variation or inability to adapt. Volunteer species under controlled conditions included Poa bulbosa and Plantago lanceolata, both of which were potential Cd-hyperaccumulating candidates. Silene aegyptiaca and Silene vulgaris were other species commonly found around zinc mines and they were grown under controlled conditions without difficulty. However, Cd concentrations in the above-ground tissues of all species mentioned above were not over the 100 mg kg-1 dry matter threshold value for hyperaccumulating cadmium.